see also [[Radiation incidents]], [[Pulmonary Embolism]], [[Trauma in pregnancy radiology]] [bear radiation safety RMH documents](bear://x-callback-url/open-note?id=E4A898AF-9A6F-4F2F-BB40-BC9410A70506), [Dunn - investigation in PE](x-devonthink-item://C2291077-3FBC-4AF0-9032-34B76AE7AE51) #tables #radiology > [!key points] overview > - adverse effects depend on the dose of radiation and gestational age > - main risk is development of subsequent malignancy; unless massive dose of radiation (eg 5-10 CT abdo pelvis in first 2 weeks of gestation or 20 therafter), no demonstrable direct effect of diagnostic radiation on fetus risk of > - miscarriage > - teratogenicity > - growth impiarmnet > - sterility - equivalent dose to an organ is the average **absorbed dose** (Gy, Grey) - energy absorbed per kg (J/kg) - A measure of the energy deposited in a medium by ionizing radiation - 1 Gy = 100 rads - usually lower in fetus than mother, unless direct path of radiation - **effective dose** (Sv) is a measure of ==overall risk from radiation== - A measure of the radiation dose to tissue that considers the different relative biological effects of different types of ionising radiation - 1 Sv = Grey x Q - (Q for e- and x-rays = 1, p+ 2, alpha 20, goes up for heavier particles) - 1 Sv = 100 rem > For radiology exposures, ==Gy and Sv are interchangeable doses==, but not for all nuclear exposures (this is because Q = 1 for x-rays) > - 1mGy = 100mrad = 1mSv > - 1 Sievert (Sv) = 100 rem # fetal radiation dose ranges - low dose ≤ 1mGy - any plain film of a body part > 10 cm from uterus - CT head or neck - *CTPA* - moderate dose = 1-10 mGy - extremely low risk of harm to fetus - CT abdo/lumbar spine - most nuclear medicine studies - high dose ≥ 10 mGy - avoid in pregnancy if possible - excess risk of childhood cancer and leukaemia of 6% per Gy - CT pelvis - PET scan - yocardial perfusion scan - dose ≥ 50mGy - may cause direct harm to fetus - *preconception* irradiation of either parents gonads does NO increase the cancer risk or malformations in thier children # Teratogenic risk - basline prevalance of any type of congeintal abnormality is ~ 3% - background radiation in Aus ~2m Sieverts/year; 6 long flights or 3 CTPA/year - actual risk only occurs with exposures well above those used for diagnostic imaging - <2/40 gestation: >50-100 mGy may cause embryonic death or implantation failure; otherwise no demonstrable effect - 2-15/40: *most vulnerable period* highest risk 8-15 weeks - neurological effects most common - non-linear dose response relationships - risk of abnormalities with dose >200 mGy - negligible risk of abnormalities below this # Cancer risk to the fetus - observed rates of malignancy lower than predicted rates from nuclear bomb survivor studies - baseline risk of developing malignancy before age 12 is ~ 1/3000 - risk to fetus of maternal compromise 2/2 an undiagnosed illness need also to be considered # contrast risk see also: [[IV contrast]] - pregnancy - *gadolinium contra-indicated* in all phases of pregnancy - however, MRI with 3 Tesla or less in any trimester is O - lactation - iodinated or gadolinium-basd contrast occasionally indicated for a breast-feeding woman - <1% administered maternal dose goes in breast milk - breast mild can be sored and used >12 hors after a V/Q scan # CTPA vs VQ scan in pregnancy table | | V/Q scan | CTPA | | ---- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | pros | - less maternal radiation to breast<br>- radiation dose reduction: omit ventilation study if perfusion normal<br>- diagnostic quality in 97% of cases<br>- can use with severe renal impairment, or iodine or contrast allergy | - less fetal radiation<br>- may demonstrate indrect signs of PE as well<br>- more distal vessels than VQ scan<br>- diagnose *alternative causes* of chest pain and review right heart strain<br>- useful in patients with underlying lung disease <br>- highly available and fast<br>- safe in pregnancy as well | | cons | - hypothetical risk to bub from radionucleotide <br>- timing and availability of scan<br>- interpretation linked to pre-test probability <br>- does not provide alternative diagnosis | - more breast radiation<br>- physiological changes in pregnancy may increase non-diagnostic rate <br>- theoretical risk of iodinated contrast to fetus | ![[Pasted image 20240321221134.png| Tintinalli table]] # radiation imaging dose tables ## estimated fetal dose (mGy) from diagnostic studies **pulmonary investigations** ![[Pasted image 20240225021340.png]] **CT in pregnancy** ![[Pasted image 20240225021424.png]] ## general doses | Imaging procedure | b/g equivalent<br>for mum | b/g equivalent<br>for bub | | ----------------------- | ------------------------- | ------------------------- | | CTB | 1 year | <1 week | | C-spine | 2 years | <1 week | | CTPA | 2-3 years | <1 month | | V/Q scan | <1 year | < 6 months | | abdomen or<br>pelvis CT | 2-3 years | 5-15 years | | lumbar XR | 1 year | 1-5 years | | nuclear bone scan | 2 years | 1-2 years | ![[Pasted image 20240225013246.png]] # Cancer risk - abdo CT in a 1 year old has lifetime cancer mortality risk of 0.18% (1/550 people) - in context of a background risk of fatal cancer of approximatly 25% - i.e. the overall CT risk in a 1 year old is approximately 1/14,000 the overall background risk - more typical range of 1/1000 to 1/10,000 depending on age and amount of radiation - 1 excess leukaemia and brain tumour occurs for every 10,000 CT scans in children aged <10 - actual figure likely lower than this - radiation dose from 1 abdo CT = 100-250 CXR